Solid-state electrolyte, solid-state battery including the electrolyte, and method of making the same

ABSTRACT

A solid-state ion conductor includes a compound of Formula 1: 
       Li (6−a)x+2y−b*z−6 A 1−x M a   x O y X b   z    Formula 1
 
     wherein, in Formula 1, A is an element having an oxidation state of +6, M is an element having an oxidation state of a, wherein a is +2, +3, +4, +5, or a combination thereof, X is an element having an oxidation state of b, wherein b is −1, −3, or a combination thereof, and 2&lt;[(6−a)x+2y−b*z−6]≤6.5,0 ≤x≤1, y&gt;0, and z≥0.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims priority to U.S. Provisional Patent Application No. 63/118,540, filed on Nov. 25, 2020, in the United States Patent and Trademark Office, and all the benefits accruing therefrom under 35 U.S.C. § 119, the content of which is incorporated herein in its entirety by reference.

FIELD

Disclosed is a solid-state ion conductor, a component for a lithium battery including the solid-state ion conductor, a positive electrode including the solid-state ion conductor, a separator for a lithium battery including the solid-state ion conductor, a lithium battery including the solid-state ion conductor, and a method of preparing the solid-state ion conductor.

BACKGROUND

Lithium metal batteries can offer improved specific energy and energy density, and in some configurations improved power density. There has been increased focus on using lithium metal as a negative electrode to improve the energy density of solid state lithium batteries. However, the lithium conductivity of available solid-state electrolytes is significantly less than liquid alternatives. Furthermore, available solid-state electrolytes that have high ionic conductivity (e.g., greater than 1 millisiemen per centimeter) are not suitably stable in the presence of lithium metal. In addition, to provide improved safety, a material which provides improved stability to air would be desirable.

Thus there remains a need for an improved solid-state lithium electrolyte, and a method of preparing the same.

SUMMARY

A solid-state ion conductor comprises a compound of Formula 1:

Li_((6−a)x+2y−b*z−6)A_(1−x)M^(a) _(x)O_(y)X^(b) _(z)   Formula 1

wherein, in Formula 1, A is an element having an oxidation state of +6, M is an element having an oxidation state of a, wherein a is +2, +3, +4, +5, or a combination thereof, X is an element having an oxidation state of b, wherein b is −1, −3, or a combination thereof, and 2<[(6−a)x+2y−b*z−6]≤6.5, 0≤x≤1, y>0, and z≥0.

A component for a lithium secondary electrochemical cell comprises a current collector; and the solid-state ion conductor on the current collector.

A positive electrode comprises a positive electrode active material; and the solid-state ion conductor on the positive electrode active material.

A separator for a lithium battery comprises a substrate; and the solid-state ion conductor disposed on a surface of the substrate.

An electrochemical cell comprises a positive electrode; a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the electrolyte comprises the solid-state ion conductor.

A method of preparing the solid state ion conductor includes contacting a lithium compound, a compound comprising an element having an oxidation state of +6, a compound comprising an element having an oxidation state of +2, +3, +4, +5, or a combination thereof, and a compound comprising an element having an oxidation state of −1, −3, or a combination thereof to provide a mixture; and treating the mixture to prepare the solid state ion conductor.

A method of manufacturing an electrochemical cell includes providing a positive electrode; disposing the solid-state ion conductor on the positive electrode; disposing an electrolyte on the positive electrode; and disposing a negative electrode on the electrolyte to manufacture the electrochemical cell.

The above described and other features are exemplified by the following figures and detailed description.

BRIEF DESCRIPTION OF THE DRAWINGS

The following figures are exemplary embodiments wherein the like elements are numbered alike.

FIG. 1 is a schematic diagram of an embodiment of a lithium battery.

FIG. 2 is a schematic diagram of an embodiment of a lithium battery.

FIG. 3 is a schematic diagram of an embodiment of a lithium battery.

FIG. 4 is a graph of intensity (arbitrary units) versus diffraction angle (°2θ) that shows the results of powder X-ray diffraction (XRD) analysis, using Cu Kα radiation, of Li_(2.125)Nb_(0.125)Te_(0.875)O₄.

FIG. 5 is an Arrhenius plot and is a graph of the diffusion coefficient of lithium (D, cm²/s) versus inverse temperature (1000/T, K⁻¹), which illustrates the ionic conductivity of Li_(2.0625)Nb0.0625Te0.9375O₄, at room temperature.

FIG. 6 is an Arrhenius plot and is a graph of the diffusion coefficient of lithium (D, cm²/s) versus inverse temperature (1000/T, K⁻¹), which illustrates the ionic conductivity of Li_(6.125)Sb_(0.125)Te_(0.875)O₆, at room temperature.

DETAILED DESCRIPTION

A solid-state lithium battery includes a negative electrode, a positive electrode, and a solid-state electrolyte between the negative electrode and the positive electrode. It is understood that the positive electrode could alternatively be referred to as a cathode, and the negative electrode as an anode. A negative electrode of interest is lithium metal for its high theoretical capacity and low voltage. Similarly, a positive electrode of interest is high-voltage nickel-manganese-cobalt oxide (NMC) for its high capacity and promise for high volumetric energy density when used in a battery. Solid-state electrolytes have been studied for use with lithium metal negative electrodes in all-solid-state batteries. However, interposing a solid-state electrolyte between a lithium negative electrode and an NMC-based positive electrode poses a number of engineering challenges, including avoiding elemental inter-diffusion between the positive electrode and solid-state electrolyte and volume changes that effect the mechanical integrity of the solid electrolyte-positive electrode interface.

Lithium transition metal oxides have been considered for use in a solid state electrolyte. However, available materials such as lithium lanthanum zirconate (LLZO) and lithium aluminum germanium phosphate (LAGP), which each have a conductivity of greater than 0.5 mS/cm at room temperature, have been previously shown to be difficult to process, and thus such materials have so far been impractical for use in lithium batteries. Thus, a processable lithium ion conductor having improved ionic conductivity is desired.

The present inventors have unexpectedly discovered that particular lithium transition metal oxides can provide improved lithium conductivity, specifically at room temperature (e.g., at 23° C.). The disclosed materials can be used to provide an improved lithium metal battery. The disclosed materials can further provide improved stability to air or moisture and can provide improved safety and stability, such as reduced likelihood of a short-circuit from a lithium metal dendrite.

Accordingly, an embodiment of the present disclosure is a solid-state ion conductor comprising a compound of Formula 1:

Li_((6−a)x+2y−b*z−6)A_(1−x)M^(a) _(x)O_(y)X^(b) _(z)   Formula 1

wherein, in Formula 1, A is an element having an oxidation state of +6, M is an element having an oxidation state of a, wherein a is +2, +3, +4, +5, or a combination thereof, X is an element having an oxidation state of b, wherein b is −1, −3, or a combination thereof, and 2<[(6−a)x+2y−b*z−6]<6.5, 0≤x≤1, y>0, and z≥0.

In an embodiment, A in Formula 1 comprises an element of Group 6, Group 8, Group 16, or a combination thereof. For example, A can be, but is not limited to, Cr, Mo, W, Fe, S, Se, Te, or a combination thereof. In a specific embodiment, A can be Te. In an embodiment, M of Formula 1 can comprise an element of Groups 2 to 17, or a combination thereof. For example, M can be, but is not limited to, Mg, Ca, Sr, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Re, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Si, Ge, Sn, P, As, Sb, S, Se, Cl, Br, I, or a combination thereof. In an embodiment, the compound of Formula 1 can include an M⁵⁺ dopant (e.g., wherein a in Formula 1 is +5). In a specific embodiment, M can be Sb, Nb, As, Ta, or a combination thereof, preferably Sb, Nb, or a combination thereof. In an embodiment, X in Formula 1 can comprise an element of Group 15, an element of Group 17, a cluster anion, or a combination thereof. For example, X can be, but is not limited to, N, F, Cl, Br, BH₄ ⁻, BF₄ ⁻, AlH₄ ⁻, NH₂ ⁻, OH⁻, SH⁻, or a combination thereof. In some embodiments, z in Formula 1 is 0 (zero), and X is excluded from the compound of Formula 1. In an embodiment, 0≤x≤1. In a specific embodiment, x=1. In an embodiment, y>0, for example 0<y≤6. In an embodiment, y=4. In an embodiment, y=6. In an embodiment, z≥0. In a specific embodiment, z =0.

The solid-state ion conductor comprising the compound of Formula 1 can have an ionic conductivity equal to or greater than of 1×10⁻⁷ siemens per centimeter (S/cm), at 23° C. For example, the solid-state ion conductor comprising the compound of Formula 1 may have an ionic conductivity of 1×10⁻⁶ S/cm to 1×10⁻² S/cm, 1×10⁻⁶ S/cm to 1×10⁻¹ S/cm, 1×10⁻⁵ S/cm to 5×10⁻² S/cm, or 1×10⁻⁴ S/cm to 1×10⁻² S/cm, at 25° C. Ionic conductivity may be determined by a complex impedance method at 20° C., further details of which can be found in J.- M. Winand et al., “Measurement of Ionic Conductivity in Solid Electrolytes,” Europhysics Letters, vol. 8, no. 5, p. 447-452, 1989, the content of which is incorporated herein by reference in its entirety.

In a specific embodiment, the solid-state ion conductor may comprise, but is not limited to, at least one of Li_(2.0625)Nb_(0.0625)Te_(0.9375)O₄, Li_(2.0625)Ta_(0.0625)Te_(0.9375)O₄, Li_(2.0625)AS_(0.0625)Te_(0.9375)O₄, Li_(2.0625)Sb_(0.0625)Te_(0.9375)O₄, Li_(6.125)Nb_(0.125)Te_(0.875)O₆, Li_(6.125)Ta_(0.125)Te_(0.875)O₆, Li_(6.125)AS_(0.125)Te_(0.875)O₆, or Li_(6.125)Sb_(0.125)Te_(0.875)O₆.

The solid-state ion conductor may have a porosity of 0% (no pores) to less than 25%, based on a total volume of the solid-state ion conductor. The porosity may be, for example, 0% to less than 25%, 1% to 20%, 5% to 15%, or 7% to 12%, based on a total volume of the solid-state ion conductor. The porosity of solid-state ion conductor may be determined by scanning electron microscopy, the details of which can be determined by one of skill in the art without undue experimentation. Alternatively, porosity may be determined using nitrogen isotherms as disclosed in E. P. Barrett, L. G. Joyner, P. P. Halenda, “The determination of pore volume and area distributions in porous substances. I. Computations from nitrogen isotherms,” J. Am. Chem. Soc. (1951), 73,373-380, the details of which can be determined by one of skill in the art without undue experimentation.

In an embodiment, the solid-state ion conductor comprising the compound of Formula 1 does not form an alloy or compound when contacted with lithium metal. Stated another way, the solid-state ion conductor comprising the compound of Formula 1 does not react with lithium metal and the solid-state ion conductor is stable when in contact with lithium metal. In an aspect, in a phase diagram containing lithium metal and the compound of Formula 1, the lithium and the compound of Formula 1 are directly connected by a tie-line, with no compounds therebetween.

A method for the manufacture of the solid-state ion conductor represents another embodiment of the present disclosure. The method includes contacting a lithium compound, a compound comprising an element having an oxidation state of +6, a compound comprising an element having an oxidation state of +2, +3, +4, +5, or a combination thereof, and a compound comprising an element having an oxidation state of −1, −3, or a combination thereof to provide a mixture, and treating the mixture to provide the compound of Formula 1. Representative lithium precursor compounds can include lithium oxide, lithium hydroxide, lithium nitrate, lithium chloride, lithium carbonate, lithium bromide, lithium azide, lithium oxalate, lithium peroxide, lithium acetate, lithium acetoacetate, or a combination thereof.

Treating of the mixture can comprise mechanochemically milling the precursor mixture. For example, the mixture can be treated by ball milling using zirconia balls in a stainless steel container. The mechanochemically milling can be conducted under an inert atmosphere, such as argon, nitrogen, helium, or a combination thereof.

Treating of the precursor mixture may alternatively or additionally comprise heat-treating the precursor mixture, for example at a temperature of 25° C. to 800° C. For example, the heat-treating may comprise heat-treating the precursor mixture at a temperature of 25° C. to 800° C., 100° C. to 775° C., 200° C. to 750° C., or 300° C. to 700° C., preferably in flowing oxygen. After heat treatment, the compound can be returned to an inert atmosphere provided by any suitable inert gas, with non-limiting examples including argon, nitrogen, helium, or a combination thereof. The heat-treating can be for a time effective to provide the compound according to Formula 1, for example 20 to 200 hours, or 25 to 150 hours, or 30 to 140 hours, or 30 to 100 hours, or 30 to 50 hours.

The disclosed method provides a solid-state ion conductor having desirable ionic conductivity. The disclosed method can also provide a cost-effective method of making the solid-state ion conductor.

The solid-state ion conductor comprising the compound of Formula 1 can be disposed on a surface of a substrate, for example, to form a component of a lithium secondary electrochemical cell. The composition comprising the solid-state ion conductor may be disposed on the surface of the substrate using any suitable means, for example, using tape casting, slurry casting, screen printing, or by pressing the solid-state ion conductor on to a surface of a current collector. Additional details of tape casting and screen printing, for example suitable binders and solvents, can be determined by one of skill in the art without undue experimentation. Alternatively, the solid-state ion conductor may be due disposed on the substrate by sputtering using a sputtering target comprising the compound of Formula 1.

In an aspect, the substrate is a current collector. The current collector may comprise, for example, at least one of nickel, copper, titanium, stainless steel, or amorphous carbon. In an embodiment, the current collector can comprise amorphous carbon.

Another aspect of the present disclosure is a positive electrode assembly. The positive electrode comprises a positive electrode active material and the solid state ion conductor comprising the compound of Formula 1 disposed on a surface of the positive electrode active material. The compound of Formula 1 may be disposed on a surface of the positive electrode active material by sputtering, for example.

The positive electrode active material can comprise, for example, a lithium transition metal oxide, or a transition metal sulfide. For example, the positive active material can be a compound represented by any of the Formulas: Li_(a)A_(1−b)M_(b)D₂ wherein 0.90≤a≤1.8 and 0≤b≤0.5; Li_(a)E_(1−b)M_(b)O_(2−c)D_(c) wherein 0.90≤a≤1.8, 0≤b≤0.5, and 0≤c≤0.05; LiE_(2−b)M_(b)O_(4−c)D_(c) wherein 0≤b≤0.5 and 0≤c≤0.05; Li_(a)Ni_(1−b−c)Co_(b)M_(c)D_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0≤α≤2; Li_(a)Ni_(1−b−c)Co_(b)M_(c)O_(2−α)X_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1−b−c)CO_(b)M_(c)O_(2−α)X₂ wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α<2; Li_(a)Ni_(1−b−c)Mn_(b)M_(c)D_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2; Li_(a)Ni_(1−b−c)Mn_(b)M_(c)O_(2−a)X_(α) wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2; Li_(a)Ni_(1−b−c)Mn_(b)M_(c)O_(2−α)X₂ wherein 0.90≤a≤1.8, 0≤b≤0.5, 0≤c≤0.05, and 0<α≤2; Li_(a)Ni_(b)E_(c); G_(d)O₂ wherein 0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, and 0.001≤d≤0.1; Li_(a)Ni_(b)Co_(c)Mn_(d)GeO₂ wherein0.90≤a≤1.8, 0≤b≤0.9, 0≤c≤0.5, 0≤d≤0.5, and 0.001≤e≤0.1; Li_(a)NiG_(b)O₂ wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; Li_(a)CoG_(b)O₂ wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; Li_(a)MnG_(b)O₂ where 0.90≤a≤1.8 and 0.001≤b≤0.1; Li_(a)Mn₂G_(b)O₄ wherein 0.90≤a≤1.8 and 0.001≤b≤0.1; QO₂; QS₂; LiQS₂; V₂O₅; LiV₂O₂; LiRO₂; LiNiVO₄; Li_((3−f))J₂(PO₄)₃ (0≤f≤2); Li_((3−f))Fe₂(PO₄)₃ wherein 0≤f≤2; and LiFePO₄, in which in the foregoing positive active materials A is Ni, Co, or Mn; M is Al, Ni, Co, Mn, Cr, Fe, Mg, Sr, V, or a rare-earth element; D is O, F, S, or P; E is Co or Mn; X is F, S, or P; G is Al, Cr, Mn, Fe, Mg, La, Ce, Sr, or V; Q is Ti, Mo or Mn; R is Cr, V, Fe, Sc, or Y; and J is V, Cr, Mn, Co, Ni, or Cu. Examples of the positive active material include LiCoO₂, LiMn_(x)O_(2x) where x=1 or 2, LiNi_(1−x)Mn_(x)O_(2x) where 0<x<1, LiNi_(1−x−y)Co_(x)Mn_(y)O₂ where 0≤x≤0.5 and 0≤y≤0.5, LiFePO₄, TiS₂, FeS₂, TiS₃, and FeS₃. For example, the positive active material can include a composite oxide of lithium and a metal selected from cobalt, manganese, and nickel. Mentioned are NMC 811 (LiNi_(0.8)Mn_(0.1)Co_(0.1)O₂), NMC 622 (LiNi_(0.6)Mn_(0.2)Co_(0.2)O₂), NMC 532 (LiNi_(0.5)Mn_(0.3)Co_(0.2)O₂), and NCA (LiNi_(0.8)Co_(0.5)Al_(0.05)O₂). The positive active material is not limited to the foregoing and any suitable positive active material can be used.

The positive active material layer may further include a conductive agent and a binder. Any suitable conductive agent and binder may be used.

A binder can facilitate adherence between components of the electrode, such as the positive active material and the conductor, and adherence of the electrode to a current collector. Examples of the binder can include polyacrylic acid (PAA), polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene-rubber, fluorinated rubber, a copolymer thereof, or a combination thereof. The amount of the binder can be in a range of about 1 part by weight to about 10 parts by weight, for example, in a range of about 2 parts by weight to about 7 parts by weight, based on a total weight of the positive active material. When the amount of the binder is in the range above, e.g., about 1 part by weight to about 10 parts by weight, the adherence of the electrode to the current collector may be suitably strong.

The conductive agent can include, for example, carbon black, carbon fiber, graphite, carbon nanotubes, graphene, or a combination thereof. The carbon black can be, for example, acetylene black, Ketjen black, Super P carbon, channel black, furnace black, lamp black, thermal black, or a combination thereof. The graphite can be a natural graphite or an artificial graphite. A combination comprising at least one of the foregoing conductive agents can be used. The positive electrode can additionally include an additional conductor other than the carbonaceous conductor described above. The additional conductor can be an electrically conductive fiber, such as a metal fiber; a metal powder such as a fluorinated carbon powder, an aluminum powder, or a nickel powder; a conductive whisker such as a zinc oxide or a potassium titanate; or a polyphenylene derivative. A combination comprising at least one of the foregoing additional conductors can be used.

The positive active material layer may be prepared by screen printing, slurry casting, or powder compression. However, the solid-state method is not limited thereto, and any suitable method may be used.

In an embodiment, the substrate may be a separator for a lithium battery, and may comprise the solid-state ion conductor comprising the compound of Formula 1 disposed on a surface of the substrate. To provide a separator, the substrate may be any suitable material. For example, to provide a separator, the substrate may comprise a polymer such as nylon, polyester, polyethylene, polypropylene, poly(tetrafluoroethylene), or polyvinyl chloride, a ceramic such as TiO₂ or yttria stabilized zirconia, or a glass such as a borosilicate glass. A combination comprising at least one of the foregoing may be used. Also, the substrate may have any suitable form, and may be nonwoven or woven material, or in the form of a film, e.g., a microporous film. Use of microporous polyethylene, microporous polypropylene, or a composite thereof is mentioned. The compound of Formula 1 may be disposed on a surface thereof, e.g., on an exterior surface, or on an interior surface, such as in a pore of the substrate.

The solid-state ion conductor disclosed herein can be incorporated into an electrochemical cell, specifically a lithium battery. Thus, another aspect of the present disclosure is a lithium battery comprising a positive electrode; a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein at least one of the positive electrode, the negative electrode, and the electrolyte comprise the compound of Formula 1. Mentioned is an embodiment wherein at least one of the positive electrode and the electrolyte comprise the compound of Formula 1.

The positive electrode can be prepared by forming a positive active material layer including a positive active material on a current collector. The positive active material and current collector can be as described above. For example, the current collector may comprise aluminum. Optionally, the solid-state ion conductor comprising the compound of Formula 1 can be disposed on the positive electrode active material, as described previously.

In an embodiment, the compound according to Formula 1 can be disposed between the positive and negative electrodes and can serve as a solid electrolyte. In an aspect, the solid electrolyte may serve as a separator to electrically insulate the positive electrode from the negative electrode. In some embodiments, the compound according to Formula 1 can be disposed on a substrate to provide a separator in the lithium battery. Suitable substrates can be as described above. In some embodiments, other electrolytes, such as a liquid electrolyte, can be excluded from the lithium battery of the present disclosure.

In an embodiment, the negative electrode can comprise, for example, lithium metal, a lithium metal alloy, or combination thereof. In an embodiment, the compound of Formula 1 is directly on the negative electrode.

A schematic diagram of a lithium battery is provided in FIG. 1. As shown in the battery 100 of FIG. 1, the negative electrode 101 can be used in combination with a positive electrode 110 and an electrolyte layer 120 can be provided between the positive electrode and the negative electrode. The battery of FIG. 1 may comprise the solid-state ion conductor of the present disclosure. The positive electrode 110 or an electrolyte layer 120 can each independently comprise the compound of Formula 1. Mentioned is use of an electrolyte layer comprising the compound of Formula 1. Also mentioned is use of a negative electrode 101 comprising the compound of Formula 1.

As shown in FIG. 2, a battery 200 may comprise a separator 230 on a solid-state electrolyte layer 240. The substrate 230 and the solid-state electrolyte layer 240, may each independently comprise the compound according to Formula 1. Also shown in FIG. 2 is a positive electrode current collector 210, a positive electrode 220 comprising the positive electrode active material, a negative electrode 250, and a negative electrode current collector 260. In an aspect, the separator 230 may be omitted and the solid-state electrolyte layer 240 may comprise the compound of Formula 1 and be suitable to electrically separate the negative electrode 250 and the positive electrode 220.

In an aspect, the solid ion conductor comprising the compound of Formula 1 can be useful as a positive active material protection layer. The positive active material protection layer, when present, can be disposed on the positive electrode and adjacent to a solid electrolyte. For example, as shown in FIG. 3, a battery 300 may comprise a solid electrolyte 330 adjacent to a positive active material protection layer 340 comprising the solid-state ion conductor including the compound according to Formula 1. Also shown in FIG. 3 is a negative electrode current collector 310, a negative electrode 320 comprising the negative electrode active material, a positive electrode 350, and a positive electrode current collector 360.

When present, the solid electrolyte in the solid electrolyte layer may be, for example, an inorganic solid electrolyte. The solid electrolyte in the solid electrolyte layer may be, for example, at least one of an oxide-containing solid electrolyte or a sulfide-containing solid electrolyte.

Examples of the oxide-containing solid electrolyte may include at least one of Li_(1+x+y)Al_(x)Ti_(2−x)Si_(3−y)P_(3−y)O₂ (where 0<x<2 and 0≤y<3), BaTiO₃, Pb(Zr_(a)Ti_(1−a))O₃ (PZT) (where 0≤a<1), Pb_(1−x)La_(x)Zr_(1−t) Ti_(y)O₃ (PLZT) (where 0≤x<1 and 0≤y<1), Pb(Mg_(1/3)Nb_(2/3))O₃—PbTiO₃ (PMN- PT), HfO₂, SrTiO₃, SnO₂, CeO₂, Na₂O, MgO, NiO, CaO, BaO, ZnO, ZrO₂, Y₂O₃, Al₂O₃, TiO₂, SiO₂, Li₃PO₄, Li_(x)Ti_(y)(PO₄)₃ (where 0<x<2 and 0<y<3), Li_(x)Al_(y)Ti_(z)(PO₄)₃ (where 0<x<2, 0<y<1, and 0<z<3), Li_(1+x+y)(Al_(a)Ga_(1−a))_(x)(Ti_(b)Ge_(1−b))_(2−x)Si_(y)P_(3−y)O₁₂ (where 0≤x≤1, 0≤y≤1, 0≤a≤1, and 0≤b≤1), Li_(x)La_(y)TiO₃ (where 0<x<2 and 0<y<3), Li₂O, LiOH, Li₂CO₃, LiAlO₂, Li₂O—Al₂O₃—SiO₂—P₂O₅—TiO₂—GeO₂, and Li_(3+x)La₃M₂O₁₂ (where M is Te, Nb, or Zr, and 0≤x≤10). Also mentioned is Li₇La₃Zr₂O₁₂ (LLZO) or Li_(3+x)La₃Zr_(2−a)M_(a)O₁₂ (M-doped LLZO, where M is Ga, W, Nb, Ta, or Al, and 0≤x≤10 and 0≤a≤2).

In an embodiment, the solid electrolyte may be a sulfide-containing solid electrolyte. Examples of the sulfide-containing solid electrolyte may include at least one of Li₂S—P₂S₅, Li₂S—P₂S₅—LiX (where X is a halogen element), Li₂S—P₂S₅—Li₂O, Li₂S—P₂S₅—Li₂O—LiI, Li₂S—SiS₂, Li₂S—SiS₂—LiI, Li₂S—SiS₂—LiBr, Li₂S—SiS₂—LiCl, Li₂S—SiS₂—B₂S₃—LiI, LiS—SiS₂—P₂S₅—LiI, Li₂S—B₂S₃, Li₂S—P₂S₅—Z_(m)S_(n) (where m and n each are a positive number, Z represents any of Ge, Zn, and Ga), Li₂S—GeS₂, Li₂S—SiS₂—Li₃PO₄, Li₂S—SiS₂—Li_(p)MO_(q) (where p and q each are a positive number, M represents at least one of P, Si, Ge, B, Al, Ga, or In), Li_(7−x)PS_(6−x)Cl_(x) (where 0≤x≤2), Li_(7−x)PS_(6−x)Br_(x) (where 0≤x≤2), or Li_(7−x)PS_(6−x)I_(x) (where 0≤x≤2).

Also, the sulfide-containing solid electrolyte may include at least sulfur (S), phosphorus (P), and lithium (Li), as component elements among the sulfide-containing solid electrolyte materials. For example, the sulfide-containing solid electrolyte may be a material including Li₂S—P₂S₅. Here, when the material including Li₂S—P₂S₅ is used as a sulfide-containing solid electrolyte material, a mixing molar ratio of Li₂S and P₂S₅ (Li₂S:P₂S₅) may be, for example, selected in a range of about 50:50 to about 90:10.

For example, the sulfide-containing solid electrolyte may include an argyrodite-type solid electrolyte represented by Formula 2:

Li⁺ _(12−n−x)A^(n+)X²⁻ _(6−x)Y⁻ _(x)   Formula 2

In Formula 2, A is at least one of P, As, Ge, Ga, Sb, Si, Sn, Al, In, Ti, V, Nb, or Ta, X is at least one of S, Se, or Te, Y is at least one of Cl, Br, I, F, CN, OCN, SCN, or N₃, and 1≤n≤5, and 0≤x≤2.

The sulfide-containing solid electrolyte may be an argyrodite-type compound including at least one of Li_(7−x)PS_(6−x)Cl_(x) (where 0≤x≤2), Li_(7−x)PS_(6−x)Br_(x) (where 0≤x≤2), or Li_(7−x)PS_(6−x)I_(x) (where 0≤x≤2). Particularly, the sulfide-containing solid electrolyte in the solid electrolyte layer may be an argyrodite-type compound including at least one of Li₆PS₅Cl, Li₆PS₅Br, or Li₆PS₅I

The solid electrolyte may be prepared by a sintering method, by melting and quenching starting materials (e.g., Li₂S or P₂S₅), or by mechanical milling. The solid electrolyte may be amorphous or crystalline. A mixture may be used.

The solid electrolyte layer may, for example, include a binder. Examples of the binder in the solid electrolyte layer may include styrene butadiene rubber (SBR), polytetrafluoroethylene, polyvinylidene fluoride, or polyethylene, but embodiments are not limited thereto, and any suitable binder may be used. The binder of the solid electrolyte may be the same as or different from a binder of the cathode active material layer and the first anode active material layer.

The solid electrolyte comprising the oxide-containing solid electrolyte or the sulfide-containing solid electrolyte may be further included in the positive active material layer, if desired.

The lithium battery can be manufactured by providing a positive electrode, providing a negative electrode, and disposing the solid-state ion conductor comprising the compound according to Formula 1 between the positive electrode and the negative electrode. The method can optionally further comprise disposing a separator between the positive and the negative electrodes. For example, the lithium battery can be manufactured by sequentially laminating the positive electrode, the solid-state ion conductor comprising the compound according to Formula 1, and the negative electrode; winding or folding the laminated structures, then enclosing the wound or folded structure in a cylindrical or rectangular battery case or pouch to provide the lithium battery.

This disclosure is further illustrated by the following examples, which are non-limiting.

EXAMPLES Example 1 Preparation of Li_(2.125)Nb_(0.125)Te_(0.875)O₄ (“doped Li₂TeO₄” or “LENTO”)

A precursor mixture was prepared by contacting LiOH, TeO₂, and Nb₂O₅ precursors in a ball mill to provide a mixture, and subjecting the mixture to heat treatment at 680° C. for 35 hours.

The reaction product was analyzed X-ray powder diffraction (XRD). The results of the XRD analysis are shown in FIG. 4, which indicate that the Nb has been doped into the structure. Impurities such a LiNbO₃ are not observed. Shown in FIG. 4 are the observed diffractions for the Li_(2.125)Nb_(0.125)Te_(0.875)O₄.

Various compositions were analyzed for phase stability and ionic conductivity. Table 1 shows the use of Nb, Ta, As, and Sb as dopants. As seen in Table 1, each composition analyzed exhibited low defect energy, increased lithium content, and high conductivity at room temperature.

TABLE 1 Energy above hull Conductivity Composition (meV/atom) (mS/cm) Li_(2.0625)Nb_(0.0625)Te_(0.9375)O₄ 5 3.5 Li_(2.0625)Ta_(0.0625)Te_(0.9375)O₄ 7 Li_(2.0625)As_(0.0625)Te_(0.9375)O₄ 16 Li_(2.0625)Sb_(0.0625)Te_(0.9375)O₄ 8 Li_(6.125)Nb_(0.125)Te_(0.875)O₆ 7 Li_(6.125)Ta_(0.125)Te_(0.875)O₆ 7 Li_(6.125)As_(0.125)Te_(0.875)O₆ 16 Li_(6.125)Sb_(0.125)Te_(0.875)O₆ 6 0.62

The ionic conductivity of Li_(2.0625)Nb_(0.0625)Te_(0.9375)O₄ and Li_(6.125)Sb_(0.125)Te_(0.875)O₆ was determined by ab-initio molecular dynamics calculation using the Vienna Ab initio Simulation Package. Relevant parameters of the calculation include a projector augmented wave potentials with a kinetic energy cutoff of 400 eV, the exchange and correlation functionals of Perdew-Burke-Ernzerhof generalized gradient (GGA-PBE), and 200 picoseconds simulation time with a time step of 2 femtosecond. The results are shown in FIGS. 5 and 6, respectively. As shown, these materials are expected to have activation energies of 0.20 electron volts (eV) and 0.26 eV, respectively. When extrapolated to 300K, the conductivity of these materials is expected to be 3.5 mS/cm and 0.62 mS/cm, respectively. These results illustrate that inclusion of a dopant, e.g., M in Formula 1, such as Nb, Ta, As, and Sb, provides an unexpected improvement in conductivity.

Various embodiments are shown in the accompanying drawings. This invention may, however, be embodied in many different forms, and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be present therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

It will be understood that, although the terms “first,” “second,” “third,” etc. may be used herein to describe various elements, components, regions, layers, or sections, these elements, components, regions, layers, or sections should not be limited by these terms. These terms are only used to distinguish one element, component, region, layer, or section from another element, component, region, layer or section. Thus, “a first element,” “component,” “region,” “layer,” or “section” discussed below could be termed a second element, component, region, layer or section without departing from the teachings herein.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “At least one” is not to be construed as limiting “a” or “an.” “Or” means “and/or.” It will be further understood that the terms “comprises” and/or “comprising,” or “includes” or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, or groups thereof.

Spatially relative terms, such as “beneath,” “below,” “lower,” “above,” “upper” and the like, may be used herein for ease of description to describe one element or feature's relationship to another element(s) or feature(s) as illustrated in the figures. It will be understood that the spatially relative terms are intended to encompass different orientations of the device in use or operation in addition to the orientation depicted in the figures. For example, if the device in the figures is turned over, elements described as “below” or “beneath” other elements or features would then be oriented “above” the other elements or features. Thus, the exemplary term “below” can encompass both an orientation of above and below. The device may be otherwise oriented (rotated 90 degrees or at other orientations) and the spatially relative descriptors used herein interpreted accordingly.

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the present disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Exemplary embodiments are described herein with reference to cross section illustrations that are schematic illustrations of idealized embodiments. As such, variations from the shapes of the illustrations as a result, for example, of manufacturing techniques and/or tolerances, are to be expected. Thus, embodiments described herein should not be construed as limited to the particular shapes of regions as illustrated herein but are to include deviations in shapes that result, for example, from manufacturing. For example, a region illustrated or described as flat may, typically, have rough and/or nonlinear features. Moreover, sharp angles that are illustrated may be rounded. Thus, the regions illustrated in the figures are schematic in nature and their shapes are not intended to illustrate the precise shape of a region and are not intended to limit the scope of the present claims.

“Group” means a group of the Periodic Table of the Elements according to the International Union of Pure and Applied Chemistry (“IUPAC”) Group 1-18 group classification system.

“Oxidation state” as used herein is a formalism used to describe a hypothetical charge that an atom would have if all bonds to atoms of different elements were 100% ionic, with no covalent component.

While a particular embodiment has been described, alternatives, modifications, variations, improvements, and substantial equivalents that are or may be presently unforeseen may arise to applicants or others skilled in the art. Accordingly, the appended claims as filed and as they may be amended are intended to embrace all such alternatives, modifications variations, improvements, and substantial equivalents. 

What is claimed is:
 1. A solid-state ion conductor comprising a compound of Formula 1: Li_((6−a)x+2y−b*z−6)A_(1−x)M^(a) _(x)O_(y)X^(b) _(z)   Formula 1 wherein, in Formula 1, A is an element having an oxidation state of +6, M is an element having an oxidation state of a, wherein a is +2, +3, +4, +5, or a combination thereof, X is an element having an oxidation state of b, wherein b is −1, −3, or a combination thereof, and 2<[(6−a)x+2y−b*z−6]≤6.5, 0≤x≤1, y>0, and z≥0.
 2. The solid-state ion conductor of claim 1, wherein A comprises an element of Group 6, Group 8, Group 16, or a combination thereof.
 3. The solid-state ion conductor of claim 2, wherein A is Cr, Mo, W, Fe, S, Se, Te, or a combination thereof.
 4. The solid-state ion conductor of claim 1, wherein A is Te.
 5. The solid-state ion conductor of claim 1, wherein M comprises an element of Groups 2 to 17, or a combination thereof.
 6. The solid-state ion conductor of claim 1, wherein M is Mg, Ca, Sr, Sc, Y, Ti, Zr, Hf, V, Nb, Ta, Cr, Mo, Re, Fe, Co, Ni, Cu, Zn, Al, Ga, In, Si, Ge, Sn, P, As, Sb, S, Se, Cl, Br, I, or a combination thereof.
 7. The solid-state ion conductor of claim 1, wherein M is Sb, Nb, or a combination thereof.
 8. The solid-state ion conductor of claim 1, wherein X comprises an element of Group 15, an element of Group 17, a cluster anion, or a combination thereof.
 9. The solid-state ion conductor of claim 1, wherein X comprises N, F, Cl, Br, BH₄ ⁻, BF₄ ⁻, AlH₄ ⁻, NH₂ ⁻, OH⁻, SH⁻, or a combination thereof.
 10. The solid-state ion conductor of claim 1, having an ionic conductivity of greater than 1×10⁻⁷ Siemens per centimeter at room temperature.
 11. The solid-state ion conductor of claim 10, having an ionic conductivity of 1×10⁻⁶ to 1×10⁻² Siemens per centimeter at room temperature.
 12. A component for a lithium secondary electrochemical cell comprising: a current collector; and the solid-state ion conductor of claim 1 on the current collector.
 13. The component of claim 12, wherein the solid-state ion conductor is in a form of a layer on the current collector.
 14. A positive electrode comprising: a positive electrode active material; and the solid-state ion conductor of claim 1 on the positive electrode active material.
 15. A separator for a lithium battery comprising: a substrate; and the solid-state ion conductor of claim 1 disposed on a surface of the substrate.
 16. An electrochemical cell comprising: a positive electrode; a negative electrode; and an electrolyte between the positive electrode and the negative electrode, wherein at least one of the positive electrode and the electrolyte comprises the solid-state ion conductor of claim
 1. 17. The electrochemical cell of claim 16, wherein the negative electrode comprises lithium metal, a lithium metal alloy, or combination thereof, and wherein the solid-state ion conductor is between the positive electrode and the negative electrode.
 18. The electrochemical cell of claim 17, wherein the solid-state ion conductor is directly on the positive electrode.
 19. A method of preparing the compound of claim 1, the method comprising: contacting a lithium compound, a compound comprising an element having an oxidation state of +6, a compound comprising an element having an oxidation state of +2, +3, +4, +5, or a combination thereof, and a compound comprising an element having an oxidation state of −1, 3, or a combination thereof to provide a mixture; and treating the mixture to prepare the compound.
 18. The method of claim 17, wherein treating the mixture comprises mechanochemical milling of the mixture to prepare a compound of Formula
 1. 19. The method of claim 17, wherein the treating is heat-treating the mixture at 25° C. to 800° C. to prepare the compound of Formula
 1. 20. The method of claim 19, wherein the heat-treating comprises heating from 300° C. to 700° C. under flowing oxygen.
 21. A method of manufacturing an electrochemical cell, the method comprising: providing a positive electrode; disposing the solid-state ion conductor of claim 1 on the positive electrode; disposing an electrolyte on the positive electrode; and disposing a negative electrode on the electrolyte to manufacture the electrochemical cell. 